High energy electrical lead-in



Jan. 6, 1959 R. w. SMITH HIGH ENERGY ELECTRICAL LEAD-IN Fil ed Jan. 15. 1954 nited States atent. E

HIGH ENERGY ELECTRICAL LEAD-IN Application January 15, 1954, Serial No. 404,282

3 Claims. (Cl. 174-152) This invention relates to a high energy electrical leadin and more particularly to a hermetically sealed lead-in adapted to feed high energy to an electrical device operating under extreme conditions of temperature and pressure.

One of the problems associated with conducting electrical energy to a device intended for operation under high vacuum is that of obtaining the hermetic seal of the lead-in conductor within the device. Where operating conditions are not too extreme and where the quantity of energy being passed is not too high, the seal of the leadin conductor has been obtained in the past by positioning th conductor in a ceramic insulator with its end secured in a compound such as glass having copper or carbon dispersed therethrough. Such compounds function as a section of the lead-in conductor by reason of the copper or carbon content, and as a sealing medium in the insulator since the glass fuses readily to the insulator and has a coefficient of thermal expansion substantially the same as that of the insulator. However, I have found that where a high energy is to be conducted, the conducting glass seal is unsatisfactory. electrical resistance of the material raises the temperature of the glass to its softening point with resultant loss of seal.

It is therefore an object of my invention to provide a hermetically sealed electrical lead-in of simple and inexpensive construction. It is another object of my invention to provide a hermetically sealed electrical lead-in capable of conducting large amounts of energy. It is another object of my invention to provide an improved method for hermetically sealing an electrical lead-in conductor within a lead-in plug.

To attain these objects, I provide a composite lead-in conductor having a highly electrically conductive metal core within a metal tube, the coefiicient of thermal expansion of the tube being substantially equal to that of the glass used in seading the conductor within the insulator.

Further objects and advantages of my invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred form of the invention is clearly shown.

The sole figure shown on the drawing is a vertical section with parts broken away of a high energy lead-in plug embodying the features of my invention.

Referring now to the drawing there is shown a leadin plug 1 adapted to be mounted in the wall of the using d vice, the plug being mounted in the Wall in any well known manner. The plug 1 comprises a metal shell 5 having a stepped bore therethrough in which a ceramic insulator 7 is positioned and maintained in gas-tight relationship with the shell. As shown, insulator 7 has a raised portion 9 thereon providing annular upper and lower shoulders 11 and 13, respectively. The lower annular shoulder 13 is seated on a correspondingly shaped annular ledge 15 formed in the shell bore, a metal sealing The heat caused by the I nickel or copper.

independent of the copper.

25, comprising 24-34% nickel, 5-25% cobalt, less than ice 2 f gasket 17 being positioned therebetween. The insulator 7 is sealed within the bore by the application of an axial load on the upper shoulder 11 in manner more fully described hereinafter.

The insulator 7 is formed with an axial stepped bore for the purpose of permitting the passage therethrough of the lead-in conductor. Since plug 1 is required to carry a high current, the conductor 19, having a relatively large cross sectional area, is formed of a material gen erally designated as a good electrical conductor, i. e'.,

As shown on the drawing, the conductor 19 comprises an upper portion 21 having copper core 23 Within a Kovar metal tube 25, the purpose of which is fully explained hereinafter, and a lower portion 27 formed of a nickel rod. The upper portion 21 is connected to a lower portion 27 in any suitable manner, i. e., brazing or welding, thus forming a single, continuous conductor capable of carrying high currents. The lower portion 27 is formed with an enlarged head portion 29 stood that in order to assure a true hermetic seal of the conductor 21 Within the insulator 7, it is essential to match the coefiicients of thermal expansion of the various coniponents and at the same time employ materials which are readily wetted by the sealing composition in order to form a tight adhesive bond therewith. The glass-seal :composition 35 has substantially the same coefiicient of thermal expansion as does the ceramic insulator 7 and is readily fusible thereto to form a composite unitary structure. This, however, is not true of the bond formed with copper. Accordingly, I have found that it was essential to provide the copper conductor with a jacket or tube 25 formed of a nickel-cobalt-iron alloy, which tube has a free sliding or spaced relationship with the copper core in order to assure that the glass seal is completely Since the Kovar metal tube 1% manganese and the remainder iron, has the desired expansion coefficient and wetting properties, and is completely sealed at the bottom to conductor 19, an efficient seal is obtained between the lead-in conductor 21 and the insulator 7. Likewise, since the electrical current is carried by the continuous copper conductor 23, the heating of the lead-in by reason of the passage of the high current is kept to a minimum and is insufficient to soften the glass seal 35.

I have found that by means of my invention, a lead in conductor capable of carrying as high as 35 amperes can be hermetically sealed within an insulator body to show no leakage at air pressures as high as 800 pounds p. s. i. In this connection, I have had excellent results with the following sealing procedure. After forming a copper conductor 23 of the desired cross section and length, a Kovar metal tube 25 is positioned thereover and the composite conductor 21 is copper-brazed into the nickel lower conductor 27 to form a continuous leadin conductor 19. In order to form a tighter bond between the glass seal composition and the Kovar tube, I have found it desirable, though not essential, to then oxidize the surface of tube 25 to a medium brown color as by application of an oxidizing gas-air flame. The lead-in conductor assembly 19 is then positioned within the stepped bore of the insulator 7 and the desired amount of glassseal composition is loaded into the insulator bore and tamped tightly about the composite conductor 21. A cylindrical ceramic, spacer 27 is then positioned within the bore about conductor 21 and the assembly is then heated to a temperature of about 1750 F. to fuse the glass. The assembly is held at this temperature for approximately five minutes, a load being applied to the top of ceramic spacer 27. The insulator temperature is then dropped slowly to below 1000 F. before releasing the load.

The sealed lead-in conductor-insulator assembly formed as described above is then positioned within the bore of shell 5 and in gas-tight relationship therewith. As shown on the drawing, an axial load is applied to the upper insulator shoulder 11 by means of a floating type pressure applicator 39, an annular spring, which is positoned on the shoulder, gasket 41 being provided therebetween. The upper end of shell is provided with internal screw threads matching those on the outer lower surface of jam nut 43, which is thus adjustable axially therein to apply load on the C spring 39, the nut 43 being positioned to abut the upper surface of an annular spacer 45 provided on the upper end of the 0 spring. A terminal screw 47 is positioned about lead-in conductor 19 and has its lower end extending into the bore of in sulator 7, screw 47 being spaced from nut 43 by a ceramic insulator sleeve 4h telescopically positioned within nut 43. A nut 51 is threaded on the upper end of terminal screw 47 and abuts the upper end of insulator 49. As shown on the drawing, insulator 49 is bonded to jam nut 43, and terminal screw 47 is bonded to insulator sleeve 49 and insulator 7 by means of a layer of silicate cement.

It is thus seen from the above description that I have provided a simple, inexpensive and efiicient hermetically sealed lead-in plug capable of conducting high current under severe pressure conditions. It is also readily apparent that my invention is also applicable to hermetically sealed electrical devices, generally.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is:

l. A hermetically sealed electrical lead-in conductor comprising a ceramic insulator having a bore therethrough, a continuous lead-in conductor positioned in the insulator bore, said conductor comprising a composite upper portion formed of a nickel-cobalt-iron alloy tube positioned in spaced relationship about a copper core, said upper portion being electrically secured to a nickel lower portion, a glass seal in said insulator bore about said tube for sealing said conductor within said bore, said tube and said insulator having coefficients of expansion substantially the same as that of said seal, said glass seal being completely independent of said copper core.

2. A hermetically sealed electrical lead-in plug comprising a shell having a stepped bore therein providing a ledge on its inner wall surface, a ceramic insulator having a stepped bore therein providing a ledge on its inner wall surface, a raised section formed on the outer surface of said insulator providing an upper and lower annular shoulder, said lower shoulder being seated on said first-mentioned ledge, a sealing gasket positioned between said ledge and said lower shoulder, a continuous lead-in conductor positioned in the insulator bore, said conductor comprising a composite upper portion formed of a nickel-cobalt-iron alloy tube positioned in free sliding relationship about a copper core, said upper portion being brazed to a nickel lower portion having an enlarged head providing a shoulder adapted to be seated on said insulator ledge, a glass-bentonite seal in said insulator bore about said tube for sealing said conductor within said bore, a ceramic spacer positioned about said tube and abutting said seal, a terminal screw positioned in the upper portion of said insulator bore and about said tube, an annular C spring positioned on said upper shoulder, an annular metal spacer positioned on the upper end of said spring, an axially adjustable jam' nut positioned in said shell in abutment with said metal spacer for applying axial pressure on said lower shoulder and sealing said insulator within said shell, and an insulator sleeve positioned about said terminal screw for separating said screw from said nut.

3. A hermetically sealed electrical lead-in conductor comprising a ceramic insulator having a bore therethrough, a continuous lead-in conductor positioned in the insulator bore, said conductor comprising a composite portion formed of a nickel-cobalt-iron alloy tube positioned in spaced relationship about a copper core, said portion being electrically secured to an electrically conductive portion, a glass seal in said insulator bore about said tube for sealing said conductor within said bore, said tube and said insulator having coefi'icients of expansion substantially the same as that of said seal, said glass seal being completely independent of said copper core.

References Cited in the file of this patent UNITED STATES PATENTS 1,471,283 Rogers Oct. 16, 1923 1,957,984 Smith May 8, 1934 2,047,302 Xardell July 14, 1936 2,293,381 Carington Aug. 18, 1942 2,307,561 Bailey Ian. 5, i943 2,651,672 Ivanoff Sept. 8, 1953 2,676,197 Read Apr. 20, 1954 

